An ideal power converter provides high efficiency and generates output waveforms that are relatively constant. This is in the ideal world. Unfortunately, switching converters are used to provide high efficiency, but generate a periodic deviation from the desired output. This periodic deviation is known as switching ripple, or simply, ripple. In the conventional application, the ripple is reduced by the use of typical filtering elements, such as inductors and capacitors, which are configured as low pass filters. For applications requiring stringent specifications on output ripple, such filters become inordinately large, very complex and extremely expensive. All of these constraints and limitations conflict with other requirements.
Recently, a more general ripple cancellation technique was conceived that applies to a broad class of switching converters. For an example of such a technique, reference is made to the paper presented at the Applied Power Electronics Conference and Exposition, 2003, APEC-03 18th Annual IEEE Volume 1, 2003, pages 464 to 470 entitled, “A Type of Ripple Current Cancellation Circuit” by M. J. Schutten, et al. This paper discloses a ripple cancellation technique that can operate with a broad class of switching converters. The circuit described in that article works to cancel the ripple in a single inductor only.
As indicated above in some cases, one can cancel ripple by filtering techniques. See, for example, an article entitled, “Novel Aspects of an Application of a Zero Ripple Techniques to Basic Converter Technologies” by J. W. Kolar, et al., Volume 1, Issue 22-27, June 1997, Power Electronics Specialist Conference, 1997 PESC 97 record, pages 796 to 803, Volume 1.
It is desirable to reduce ripple in a more economical and efficient way. In the present invention, a passive ripple cancellation circuit is employed to reduce the output ripple of a current doubler rectifier. A current doubler rectifier is often advantageous when a high output current and a low voltage is desired. Versions of the ripple cancellation circuit, according to embodiments of this invention, apply to current doublers.